Bronstein S M, Cochrane J E, Craft T R, Swenberg J A, Skopek T R
Department of Pathology, Duke University, Durham, North Carolina 27710.
Cancer Res. 1991 Oct 1;51(19):5188-97.
We examined the toxicity, mutagenicity, and mutational spectra of N-ethyl-N-nitrosourea (ENU) in three Epstein-Barr virus-transformed human lymphoblastoid cell lines, each with a different DNA repair phenotype. One cell line lacks O6-alkylguanine-DNA alkyltransferase (AGT) activity; another, derived from a patient with xeroderma pigmentosum, complementation group A, lacks nucleotide exicision repair (NER) capability, and the third is competent in both repair functions. ENU-induced toxicity and mutagenicity at the hypoxanthine-guanine phosphoribosyltransferase locus were increased to a similar degree relative to the repair-competent cells in both AGT-deficient and NER-deficient cells. We determined the mutational spectra for ENU by identifying DNA sequence changes at the hypoxanthine-guanine phosphoribosyltransferase locus in at least 26 clones resistant to 6-thioguanine from each cell line. Of the characterized mutations, 89% were single-base pair substitutions. Transitions and transversions were found at AT and GC base pairs in all three cell lines. The biggest difference within the spectra was in the rate of transitions at GC base pairs. Compared to the repair-competent cell line, this mutation was elevated about 8-fold in the AGT-deficient cells and about 3-fold in the NER-deficient cells. We conclude that both AGT and NER play an important role in protecting human cells from the toxic and mutagenic effects of ENU. Furthermore, the mutational spectra suggest that both of these repair systems participate in the repair of O6-ethylguanine adducts.
我们研究了N-乙基-N-亚硝基脲（ENU）在三种爱泼斯坦-巴尔病毒转化的人类淋巴母细胞系中的毒性、致突变性和突变谱，每个细胞系都有不同的DNA修复表型。一个细胞系缺乏O6-烷基鸟嘌呤-DNA烷基转移酶（AGT）活性；另一个来源于着色性干皮病A互补组患者的细胞系缺乏核苷酸切除修复（NER）能力，第三个细胞系则具备这两种修复功能。相对于具有修复能力的细胞，ENU在AGT缺陷型和NER缺陷型细胞中，在次黄嘌呤-鸟嘌呤磷酸核糖基转移酶位点诱导的毒性和致突变性均有相似程度的增加。我们通过鉴定来自每个细胞系的至少26个对6-硫鸟嘌呤耐药的克隆在次黄嘌呤-鸟嘌呤磷酸核糖基转移酶位点的DNA序列变化，来确定ENU的突变谱。在已鉴定的突变中，89%是单碱基对替换。在所有三个细胞系的AT和GC碱基对处均发现了转换和颠换。谱内最大的差异在于GC碱基对处的转换率。与具有修复能力的细胞系相比，这种突变在AGT缺陷型细胞中升高了约8倍，在NER缺陷型细胞中升高了约3倍。我们得出结论，AGT和NER在保护人类细胞免受ENU的毒性和致突变性影响方面都起着重要作用。此外，突变谱表明这两种修复系统都参与了O6-乙基鸟嘌呤加合物的修复。
